Pressure-sensitive adhesives, which are normally tacky materials adherent upon application of light pressure, are desirable in a number of industrial applications because they can be used with various materials and are easily adapted to production line techniques. In order to function satisfactorily as a pressure-sensitive adhesive, a composition must provide a combination of properties including good tack, adhesion and cohesive strength, and must adhere instantaneously when applied to substrates of differing surface characteristics. To be useful in many industrial applications, the bond obtained by the use of the adhesive must have sufficient strength to remain firm over relatively long periods and under different and sometimes severe environment conditions.
Most pressure-sensitive adhesives, however, have low relative strength as compared, for instance, to thermosetting resin adhesives, because the desired tack and adhesive properties are ordinarily inconsistent with the high level of cohesive strength obtained with other types of thermosetting resin adhesive polymers. Because of this, attempts to provide pressure-sensitive adhesives having improved cohesive strength have not proven satisfactory, with continuing problems being the tendency of the adhesive to lose strength upon aging and the unsatisfactorily low tack and adhesion which tend to be found with higher strength adhesives of this type.